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Irritable Bowel Syndrome Causes and Symptoms


What Causes IBS?

The colon, which is about 6 feet long, connects the small intestine with the rectum and anus. The major function of the colon is to absorb water and salts from digestive products that enter from the small intestine. Two quarts of liquid matter enter the colon from the small intestine each day. This material may remain there for several days until most of the fluid and salts are absorbed into the body. The stool then passes through the colon by a pattern of movements to the left side of the colon, where it is stored until a bowel movement occurs.

Colon motility (contraction of intestinal muscles and movement of its contents) is controlled by nerves and hormones and by electrical activity in the colon muscle. The electrical activity serves as a "pacemaker" similar to the mechanism that controls heart function.

Movements of the colon propel the contents slowly back and forth but mainly toward the rectum. A few times each day strong muscle contractions move down the colon pushing fecal material ahead of them. Some of these strong contractions result in a bowel movement.

Because doctors have been unable to find an organic cause, IBS often has been thought to be caused by emotional conflict or stress. While stress may worsen IBS symptoms, research suggests that other factors also are important. Researchers have found that the colon muscle of a person with IBS begins to spasm after only mild stimulation. The person with IBS seems to have a colon that is more sensitive and reactive than usual, so it responds strongly to stimuli that would not bother most people.

Ordinary events such as eating and distention from gas or other material in the colon can cause the colon to overreact in the person with IBS. Certain medicines and foods may trigger spasms in some people. Sometimes the spasm delays the passage of stool, leading to constipation. Chocolate, milk products, or large amounts of alcohol are frequent offenders. Caffeine causes loose stools in many people, but it is more likely to affect those with IBS. Researchers also have found that women with IBS may have more symptoms during their menstrual periods, suggesting that reproductive hormones can increase IBS symptoms.

Researchers have determined that IBS patients have elevated food-specific IgG4 antibodies to common foods such as wheat, beef, pork, lamb, and soya bean. These findings are published in the July 2005 issue of The American Journal of Gastroenterology.

What Are the Symptoms of IBS?

If you are concerned about IBS, it is important to realize that normal bowel function varies from person to person. Normal bowel movements range from as many as three stools a day to as few as three a week. A normal movement is one that is formed but not hard, contains no blood, and is passed without cramps or pain.

People with IBS, on the other hand, usually have crampy abdominal pain with painful constipation or diarrhea. In some people, constipation and diarrhea alternate. Sometimes people with IBS pass mucus with their bowel movements. Bleeding, fever, weight loss, and persistent severe pain are not symptoms of IBS but may indicate other problems.

How Is IBS Diagnosed?

IBS usually is diagnosed after doctors exclude the presence of disease. To get to that point, the doctor will take a complete medical history that includes a careful description of symptoms. A physical examination and laboratory tests will be done. A stool sample will be tested for evidence of bleeding. The doctor also may do diagnostic procedures such as x-rays or endoscopy (viewing the colon through a flexible tube inserted through the anus) to find out if there is disease.


References and Sources: Medline, Pubmed, National Institutes of Health

last update: June 2006


This information is not intended to be a substitute for professional medical advice. You should not use this material to diagnose or treat a health condition or disease without consulting with your healthcare provider.
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